Conversion of hydrocarbons into gaseous olefins



NOV. 10, 1 942. KLEIN ETAL 2,301,727

CONVERSION OF HYDROGARBONS INTO GASEOUS OLEFINES Filed Feb. 18, 1939 R2I I? 000000 odflao INVENTORS TH EIR ATTORNEYS Patented Nov. 10, 1942CONVERSION OF HYDROCABBONS INTO GA'SEOUS OLEFINS Hans Klein, Mannheim,Ludwlgshafen on the Mannh Hoi'editl,

Ferdinand Haubach, -Bhine, and Wilhelm elm, Germany; vested in the AllenProperty Custodian Application February 18 In Germany F 1 Claim.

The present invention relates to improvements in the production ofgaseous olefins from hydrocarbons.

It has already been proposed to prepare gaseous olefins by the action ofoxygen on saturated hydrocarbons at elevated temperature, the oxygen, inorder not to obtain the formation of flame and reaction to formacetylene, being kept within certain limits which vary according to thenature of the saturated initial hydrocarbons and the height of thepressure; in the case of propane and'when working at ordinary pressureup to about 30 per cent by volume of oxygen are added with reference tothe mixture, in the case of ethane somewhat more, in the case of butanesomewhat less. In spite of these limited amounts of oxygen, however, thereaction frequently proceeds very turbulently at first, whereby theyields of gaseous olefins are impaired. To counteract this it hasalready been proposed to work in vacuo. This does indeed prevent theyields of olefins being reduced by overheating, but on the other hand ithas the efiect that the reaction of the hydrocarbons with the oxygendoes not proceed completely in the usual apparatus so that either anunusually long reaction chamber must be used or a certain oxygen contentin the final product must be taken into account.

We have now found that in the reaction of saturated hydrocarbons havingmore than one carbon atom in the molecule with oxygen to form gaseousoiefins all the said drawbacks can be avoided and that good yields ofgaseous olefins and final gases containing only a small amount of oxygencan be obtained even when working at atmospheric pressure or slightlyreduced pressure, as for example about 0.6 atmosphere, by adding amountsof oxygen with which at the prevailing pressure there is no formation offlame and consequently no appreciable formation of acetylene and using areaction chamber of which the first part has a considerably smaller freecross-section than the following part. Whereas in the known cases thetemperature in the reaction chamber measured in the direction of thefiowing gases rises very quickly, according to this invention it risesmuch more slowly and also falls, after reaching its maximum value, muchmore slowly generally speaking in the second part of the chamber than inthe known cases.

By reason of the smaller cross-section, the gas mixture in reactionchambers of the said shape fiows in the first part at a considerablyhigher speed than in the following part. In this way overheating of theapparatus is avoided by the 1939, Serial No. 257,120 ebruary 22, 1938 Iwith the hydrocarbons the oxygen is given sufilcient time to act on thehydrocarbons, so that final gases practically free from oxygen areobtained.

The efiect of working according to this invention may be seen from thefollowing comparisons:

1. parts by volume of ethane and 25 parts of oxygen are heated to about600 C. either separately or, when using a non-metallic, for instanceceramic constructional material, jointly, and then fiow at a speed of1.2 meters per second while the temperature rises to about 850 C.through a reaction tube which throughout its whole length has anunchanged cross-section for the passage of gas. A final gas is obtainedwhich contains 25 per cent of ethylene and 0.8 per cent of oxygen.

2. If the initial mixture be led in the same way at a speed of 6 metersper second through the same reaction tube while the temperature rises toabout 750 C., the yield of ethylene is increased to 30 per cent but thefinal gas mixture contains 3.2 per cent of oxygen.

3. If the same gas mixture be led at a speed of 6 meters per secondthrough the first part of a reaction tube and then at less than halfthis speed of fiow through the second part of the reaction tube the freecross-section of which, according to this invention, is about two and ahalf times as great as that of the first part, the temperature in thefirst part rising to 750 and in second part to 850 C., the yield ofethylene rises to 32 per cent and the final gas mixture contains only0.9 per cent of oxygen.

According to this invention it is thus possible to produce a practicallycomplete reaction of the oxygen with the hydrocarbons, which is ofimportance not only on economical grounds but also for the further useof the resulting gases, and furthermore a yield of unsaturatedhydrocarbons is obtained which is considerably higher than that obtainedwhen working at lower speed of fiow (1), because in the latter case bythe rapid rise of the temperature in the reaction chamber by reason ofthe turbulent reaction of hydrocarbons with oxygen the yield ofunsaturated hydrocarbons is impaired.

The small cross-section for the passage of gas in the first part of thereaction chamber may not only be produced by appropriate shaping of thereaction vessel but also by introducing filler bodies into the same. Thesame result is obtained by building in gratings or by lining the wallsof the reaction chamber. For the said insertions or filler bodies it ispreferable to use materials which do not influence the reaction, as forexample clay, quartz or silimanite. In the first part oi. the reactionchamber it is preferable to use filler bodies of small resistance; inthe second part oi the reaction chamber filler bodies of higherresistance may also be used. In all cases care should be taken that nodead corners occur in the reaction chamber.

Figures 1 and 2 of the accompanying drawing show diagrammatically twoarrangements of reaction tubes adapted for the process according to thisinvention by way of example, but the invention is not restricted tothese two arrangements.

The preheated mixture of hydrocarbons and oxygen passes through a supplyconduit Z, Figure 1, into the first part R1 of the reaction chamberwhich is filled with rods, for example of ehamotte. After a part of theoxygen has reacted with the hydrocarbons at high speed of gas flow inthe said first part, the gas mixture flows through a wider second partR2 of the reaction chamber which is filled with balls, for example ofporcelain and in which at smaller speed of flow of the gas the residualpart of the oxygen acts on the hydrocarbons. The final gas mixtureleaves the reaction chamber at A.

Referring to Figure 2, the smaller cross-section in the first part R1 ofthe reaction chamber is produced by a built-in displacement body V.

The alteration of the cross-section, instead of being as shown in thedrawing, may also be gradual, and instead a unitary reaction chamber onewhich is subdivided, for example into channels. may be used.

The hydrocarbons to be reacted, as for example ethane or propane, aremixed with oxygen in a ratio oi! from about to parts by volume to from20 to 30 parts by volume. The initial gases, before introduction intothe reaction chamber, are heated to at least about 450 C. In the firstpart of the reaction chamber the temperature rises to more than about700 C. by the heat set free by the reaction. In the second part thetemperature is kept at about 800 C. or more. Generally speaking externalheating is unnecessary.

The gas mixtures obtained contain only about 0.4 to l per cent ofoxygen, whereas in a reaction tube of equal length ilnal gases having anoxygen content or several per cent are obtained by the processeshitherto known with the same speed of flow.

What we claim is:

A process for the production of gaseous oleflns by the action of oxygenon hydrocarbons at elevated temperature, the oxygen bein used in suchamounts that at the prevailing pressure there is no formation of aflame, which comprises passing the heated mixture of said hydrocarbonswith said oxygen through the first part of a reaction zone at a highspeed 01' flow and through the iollowing part at a lower speed of flow,the speed of flow of the gas mixture being regulated by using a reactionzone the first part of which has an appreciably smaller freecross-section than the following part.

HANS KLEIN. FERDINAND HAUBACH. WILHELM HOFEDI'IZ.

